Arc-extinguishing circuit breaker with enclosed gas space



Nov. 16, 1965 H. FORWALD 3,218,420

ARC-EXTINGUISHING CIRCUIT BREAKER WITH ENCLOSED GAS SPACE Filed Sept.25, 1962 M W aaii 3 2 111 7 ,13 4 1o 12 R \W L INVENTOR. f v or wn JLM-a m 0, 012

A773rwys United States Patent 3,218,420 ARC-EXTINGUISHING CIRCUITBREAKER WITH ENCLOSED GAS SPACE Haakon Forwald, Ludvika, Sweden,assignor to Allmiinna Svenska Elektriska Aktiebolaget, Vasteras, Sweden,a

corporation of Sweden Filed Sept. 25, 1962, Ser. No. 226,076 Claimspriority, application Sweden, Oct. 4, 1961, 9,839/ 61 3 Claims. (Cl.200-148) Circuit breakers are known having a gas quantity consisting offor example sulphur hexafluoride (SF 6) permanently enclosed in anextinguishing chamber. In such circuit breakers the arc gases are notremoved from the extinguishing chamber since to a great extent they arereconverted to the gas originally used. Reasonable breaking effects canbe obtained by mechanically effecting an air blast on the breaking gapby means of momentary compression of part of the gas enclosed in theextinguishing chamber.

The present invention relates to a circuit breaker having a completelyclosed extinguishing chamber filled with gas and comprising a stationaryand a movable contact. The invention is characterised in that theextinguishing chamber is formed as a pump housing in which a pistonwhich divides the extinguishing chamber into an arc chamber containingthe stationary contact and a pressure generating chamber is arranged tobe moved forward biased by the movable contact. This is passed throughthe piston and provided with a carrier whose distance from a first stopin the piston in the closed position of the breaker is so chosen thatthe tip of the movable contact must be completely drawn into the pistonbefore the carrier meets the first stop. An extinguishing gas channel isarranged through the piston, which channel is closed in the closedposition of the circuit breaker by the movable contact, but is open whenthe carrier has reached the first stop in the piston.

By means of the invention an increased breaking capacity is obtained forbreakers of the above mentioned type through intensified are blowing. Inaddition to a compression of the gas in the pressure generating chamber,and under pressure is obtained in the arc chamber and the diflerence ispressure on both sides of the piston will be great and thus theextinguishing gas flow generated by this pressure difference will bepowerful. The invention also provides a relative decrease in the work ofthe arc and the breaking gas development since the are for aconsiderable part of its length will burn in a space having lowpressure.

Another advantage with the construction is that during the openingmovement when the carrier has reached the stop in the piston, themovable contact and the extinguished air channel are in rest positionrelative to each other and thus the arc is exposed to an intensive blastat one base point during almost the entire breaking process.

In order to direct a fiow of extinguishing gas towards the base of thearc from all sides the tip of the movable contact is arranged to form anannular slot with the opening in the piston for the movable contact,which slot is in communication with the extinguishing air channel. It isfurther suitable to provide the piston with a second stop which is metby the carrier when the circuit breaker is closed, whereby the distancebetween the stops is chosen so that when the circuit breaker is closedthe volume of the arc chamber will be as small as possible. In this wayit is ensured that as low a pressure as possible is generated in the arcchamber at a breaking action.

To prevent a gas pocket being compressed in the arc, chamber, which gaspocket, when the circuit breaker is 'ice closed, prevents or delays theclosing, it is suitable to arrange a by-pass channel through the pistonand provide this channel with nonreturn valve allowing gas to flow gromthe arc chamber to the pressure generating cham- The accompanyingdrawing shows one embodiment of the invention. In the FIGURE 1designates the breaker support to which the extinguishing chamber 2 isattached by means of insulators 3 and 4. A stationary contact 5 isarranged at the bottom of the extinguishing chamber. The movable contact6 passes through the piston 7 which slides in an air-tight manner in theextinguishing chamber 2 formed as a pump housing. The movable contact isoperated by means of a lever system of insulating rods 8. The movablecontact is provided with a carrier 9. Two stops are also arranged in thepiston, namely a first stop 10 and a second stop 11. Further, anextinguishing gas channel 12 and a by-pass channel 13 provided with anonreturn valve 14. The are chamber is formed by the space 15 and thepressure generating chamber by the space 16. The extinguishing chamber 2is filled with sulphur hexafluoride.

An important feature of the present invention is that the volume of thearc chamber or space 15 in the closed position of the breaker is verysmall compared to the volume of the pressure generating chamber or space16.

To explain this more clearly, it should be noted that, in order toensure an extinguishing of the arc, the gas should flow through the gaschannel 12 in the piston at the speed of sound. This speed is obtainedwhen the pressure on one side of the piston is twice as great as thepressure on the other side of the piston, that is the side limiting thespace into which the gas flows. In the breaker of this invention, thepressure in the space 15 decreases to half its initial value when thisspace 15 is doubled, if the assumption is made that during this firstpart of the breaking movement very little gas flows through the channel12. As the piston will have to move only a small distance in order tocause a doubling of space 15, the pressure in space 16 will, during thisfirst part of the breaking operation, remain unchanged substantially.Thus a condition necessary for a flow of extinguishing gas through thechannel 12 at the speed of sound will be achieved at the beginning ofthe breaking movement of the movable contact.

At an opening movement the movable contact 6 is moved upwards until thecarrier meets the stop 10. Only then does the piston 7 begin to move anda flow of extinguishing gas passes through the channel 12 which is nowfreed by the movable contact pin 6. Thus a powerful flow ofextinguishing gas hits the are between the contacts 5 and 6 andparticularly the tip of the movable contact is cooled considerably bythe flow of extinguishing gas. In the upper part of the extinguishingchamber 2 a piston is inserted in dotted lines to show the circuitbreaker in its open position.

The circuit breaker is closed by the movable contact 6 moving downwards,whereby the carrier 9 meets the second stop 11 and the movable contactcloses the extinguishing air channel 12. The piston now moves downwardswith the movable contact 6. The gas in the arc chamber 15 is thuscompressed and in order to prevent the compression becoming too greatchannels 13, as mentioned earlier, have been arranged. Thus gas nowflows from the arc chamber to the pressure generating chamber throughthe channel 13 past the nonreturn valve 14, and a pressure equalizationoccurs between the arc chamber and the pressure generating chamber 16.The stops 10 and 11 have been placed at such a distance from each otherthat at closed breaking gap the piston 7 almost touches the bottom ofthe extinguishing chamber so that in the closed position of the circuitbreaker the arc chamber 15 has a very small volume. The normal pressurein the extinguishing chamber 2 may be atmospheric pressure, but it mayalso have other values, for example, a couple of atmospheresover-pressure. In this case flexible gas sealings are suitably arranged'for the passage of the movable contact through the upper wall of theextinguishing chamber.

I claim:

1. A circuit breaker comprising a completely closed extinguishingchamber filled with gas and having a closed cylindrical portion, apiston slidable in the cylindrical portion and dividing the chamber intoan arc chamber having an end wall and a pressure generating chamber, thecross-section of the piston at the end nearest said end wall being equalto the internal cross-section of the closed cylindrical portion, astationary contact within the arc chamber, a movable contact passingthrough said piston, said piston being slidably mounted on the movablecontact, means for moving the movable contact from and towards thestationary contact, said movable contact and piston having cooperatingmeans thereon for limiting the sliding movement of the piston withrespect to the movable contact between first and second limit positions,said movable contact having a tip, the tip of the movable contact beingcompletely drawn into the piston when said piston reaches one of saidlimit positions during opening movement, said piston having anextinguishing gas channel therethrough, said movable contact closingsaid gas channel in the closed position of the circuit breaker, saidcooperating means including means allowing said movable contact, as itfirst moves away from the stationary contact, to slide in said piston toan extent sufficient to uncover said gas channel, said cooperating meansfurther including means to move said piston with the movable contactduring further movement of the movable contact away from the stationarycontact, said piston, when said contacts are closed and said piston isin the second limit position, lying closely adjacent the end wall of thearc chamber.

2. In a circuit breaker according to claim 1, said piston having anannular slot exposed by the tip of the movable contact when said pistonreadies said first limit position forming a part of the extinguishinggas channel.

3. In a circuit breaker according to claim 1, said piston having aby-pass channel therethrough provided with a non-return valve allowinggas to flow from the arc chamber to the pressure generating chamberonly.

References Cited by the Examiner UNITED STATES PATENTS 2,246,171 6/1941Grosse 200l48 2,781,435 2/1957 Heilmann et al 200150 2,957,063 10/1960Leeds 200-448 FOREIGN PATENTS 671,326 2/ 1939 Germany.

784,373 10/1957 Great Britain.

KATHLEEN H. CLAFFY, Primary Examiner.

ROBERT K. SCHAEFER, BERNARD A. GILHEANY,

Examiners.

1. A CIRCUIT BREAKER COMPRISING A COMPLETELY CLOSED EXTINGUISHINGCHAMBER FILLER WITH GAS AND HAVING A CLOSED CYLINDRICAL PORTION, APISTON SLIDABLE IN THE CYLINDRICAL PORTION AND DIVIDING THE CHAMBER INTOAN ARC CHAMBER HAVING AN END WALL AND A PRESSURE GENERATING CHAMBER, THECROSS-SECTION OF THE PISTON AT THE END NEAREST SAID END WALL BEING EQUALTO THE INTERNAL CROSS-SECTION OF THE CLOSED CYLINDRICAL PORTION, ASTATIONARY CONTACT WITHIN THE ARC CHAMBER, A MOVABLE CONTACT PASSINGTHROUGH SAID PISTON, SAID PISTON BEING SLIDABLY MOUNTED ON THE MOVABLECONTACT, MEANS FOR MOVING THE MOVABLE CONTACT FROM AND TOWARDS THESTATIONARY CONTACT, SAID MOVABLE CONTACT AND PISTON HAVING COOPERATINGMEANS THEREON FOR LIMITING THE SLIDING MOVEMENT OF THE PISTON WITHRESPECT TO THE MOVABLE CONTACT BETWEEN FIRST AND SECOND LIMIT POSITIONS,SAID MOVABLE CONTACT HAVING A TIP, THE TIP OF THE MOVABLE CONTACT BEINGCOMPLETELY DRAWN INTO THE PISTON WHEN SAID PISTON REACHES ONE OF SAIDLIMIT POSITIONS DURING OPENING MOVEMENT, SAID PISTON HAVING ANEXTINGUISHING GAS CHANNEL THERETHROUGH, SAID MOVABLE CONTCT CLOSING SAIDGAS CHANNEL IN THE CLOSED POSITION OF THE CIRCUIT BREAKER, SAIDCOOPERATING MEANS INCLUDING MEANS ALLOWING SAID MOVABLE CONTACT, AS ITSFIRST MOVES AWAY FROM THE STATIONARY CONTACT, TO SLIDE IN SAID PISTON TOAN EXTEND SUFFICIENT TO UNCOVER SAID GAS CHANNEL, SAID COOPERATING MEANSFURTHER INCLUDING MEANS TO MOVE SAID PISTON WITH THE MOVABLE CONTACTDURING FURTHER MOVEMENT OF THE MOVABLE CONTACT AWAY FROM THE STATIONARYCONTACT, SAID PISTON, WHEN SAID CONTACTS ARE CLOSED AND SAID PISTON ISIN THE SECOND LIMIT POSITION, LYING CLOSELY ADJACENT THE END WALL OF THEARCCHAMBER.